The aim of the present invention is to rationalise and improve the realisation of the screws in order to reduce to a minimum the drawbacks which obtain during use of the screws themselves, such as for example the encrustations which form on the screw and on the containing structure, the blocking of holes (if present) in the containing structure, blockages which can occur at the screw outlet, problems connected with wear and with the replacement of the various parts constituting the screw and the containing structure.
An advantage of the invention is that it improves the distribution of the product exiting from the terminal part of the screw.
A further advantage of the invention is that it optimises the power needed to operate the screw, and consequently optimises use of the driving power needed to operate the screw.